One type of three-dimensional integrated circuit (3D IC) is made using a number of semiconductor die stacked vertically and bonded to create the individual 3D ICs. Electrical connections from external bond pads to electrical conductors of the 3D ICs, and between electrical conductors of different layers of the 3D ICs, can be made using various methods. For example, in one wirebonding method the edges of adjacent chips can be staggered in a stair step fashion. This permits external bonding wires to be connected between pads on the chip and pads on a substrate.
Another method for making electrical connections between stacked chips, called through-silicon via (TSV), has generated significant interest. Interconnecting stacked chips by TSV has several advantages over conventional external wirebonding techniques. A stacked chip with TSV can exhibit a wider bandwidth and thus greater input/output compared to stacked chips connected via external wirebonding techniques. With TSV there is a shorter connection path which enhances speed and lowers power consumption.
TSV can be accomplished using wafer scale stacking with the aligned die separated or diced later. This provides for lower-cost, high throughput but it suffers from yield problems because the failure of one chip in a stack of chips causes that stack to fail resulting in lower yields. In addition, handling thinned down wafers is a manufacturing challenge that can result in damaged or destroyed product. TSV can also be accomplished using die scale stacking. This has the advantage that handling is relatively easy but at the expense of high cost.
Another disadvantage of conventional TSV is that a typical TSV process requires 11 steps for each die or wafer: TSV photoresist deposition, TSV etching, silicon dioxide deposition, barrier seed deposition, photoresist patterning, Cu/W deposition, photoresist removal, Cu/W chemical mechanical polishing, support/handling die bonding, die thinning, and bonding. In addition to the time and expense required for all the steps, the required handling and processing of each die results in lower yields.